The goals of this project are to characterize lymphocyte Fc receptors genetically and functionally. Recent findings indicate that the Fc receptors of B cells and T cells but not UL cells nor macrophages are associated with Ia antigens. In addition, a subpopulation of UL cells, the effector cells in antibody-dependent cell-mediated cytotoxicity was shown not to bear Ia antigens. In the case of the B cell, the Fc receptors and Ia antigens appear to be distinct molecules, and the association appears to be ligand induced. There is also a single non-H-2 locus which determines antigens associated with the Fc receptor. In one haplotype, this locus has been shown to be linked to the M locus. These findings indicate that Fc receptors may play a key role in immunoregulation. BIBLIOGRAPHIC REFERENCES: Dickler, H.B.: Lymphocyte binding of aggregated immunoglobulin. Scand. J. Immunol. Suppl. 5: 91-97, 1976. Arbeit, R.D., Henkart, P.A. and Dickler, H.B.: Lymphocyte binding of heat-aggregated and antigen-complexed immunoglobulin. In Bloom, B. and David, J.R. (Eds.): In Vitro Methods in Cell Mediated and Tumor Immunity; New York, Academic Press, 1976, pp. 143-154.